To sell or not to sell - that is the question

[Joseph Shapiro]

Hey gang!

I have an apartment building in the northeast.  Bought it 5 years ago.  

Currently, cashflow is **** - $1,500/month but if I increase rents to the current market (probably a 2 - 3 year process) I can likely cashflow $4,000/month.  This accounts for a tax reassessment and refinancing the current mortgage balance (loan is comprised of two 5 year terms).
I have $600,000 in the building (between downpayment, capex, closing costs etc).

I have the opportunity to sell it right now and gross $1M or after taxes $700K (if I can't 1031).

Question: Would you sell or keep this property?